So, here’s more or less the case for the assertion that Mark Zuckerberg is an INTJ rather than an ENTJ (and INTP – read on):

1) He is universally described as an introvert by those who know him, often using that exact term.

2) Before Facebook became a success, his habit was to move from project to project as the mood struck. Even after Facebook was on its way, he endangered the company and diverted valuable time and manpower to working on a new project (Wirehog) which had taken his interest. He did this despite the strident pleas of Sean Parker and others in the company who wanted to keep him focused on Facebook. This suggests dominant Ni, not dominant Te.

3)  Unusually for a startup CEO, he did very little talking during presentations to investors, preferring instead to leave that to Sean Parker. Typically, the CEO of a supplicant startup does most of the talking to show off his fitness to lead, pausing only briefly to let the subordinate members of his team get a few words in. Zuckerberg was apparently entirely assured that he could get the investment he needed, and was instead vetting the investors for worthiness to partake in Facebook. Here again, I am inclined to doubt that his dominant function is Te.

4)  He was extremely reluctant to permit mere business concerns to trump over aesthetic/design concerns, which resulted in a conflict with Eduardo Saverin over the role of advertising on the site that ended with Saverin’s ejection from the company and a lawsuit. Even years later when Sheryl Sandberg took over as COO, he was deeply wary of advertising and only begrudgingly accepted that it was necessary if Facebook was to be a lasting business. (Sandberg, by the way, managed to drive home this point only after asking everyone to describe what exactly Facebook’s business would be if not advertising. No one could think of anything else.) He strikes me as rather too disinterested in business matters to prefer Te to Ni (contrast that with Bill Gates). He has always prioritized his vision for the site’s minimalist aesthetic and usability over the need to make money or establish Facebook as a business.

5) He noted in an interview that the critical failure of The Social Network was the inability of its creators to comprehend that someone could build something for the sake of the thing itself rather than to further some pleasure-seeking motive like getting rich or getting laid. This, again, makes me think Te is of secondary rather than primary importance to him, and that what’s really important to him is the internal world.

6) Zuckerberg kept a leather notebook full of his ideas for the future direction of Facebook. He called it “The Book of Change,” and the inside cover was emblazoned with the Gandhi quote “you must be the change you wish to see in the world.” Few people besides Zuckerberg were permitted to read the Book of Change. Apparently the writing frequently lapses into a stream-of-consciousness style, including one part quoted in The Facebook Effect in which Zuckerberg stopped mid-sentence and noted in the margin, “this doesn’t seem to be going anywhere.” The book, by the way, was not merely an ordinary notebook like you might buy at Wal-Mart or wherever, but rather something that “looked like what Chairman Mao would carry around.” Didn’t someone say something about Ni-dominant personalities speaking in oracular tones?

7) Zuckerberg was particularly bad at communicating with his employees and executives in the early years. He refused to let anyone see his notes in the “Book of Change”, and investor Kevin Efrusy recounts that when he  “told him the point was to communicate to everyone else,” Zuckerberg “looked at me like that was a new thought and said, ‘Oh really?’” The company was for a long time in a state of near-constant chaos precisely because Zuckerberg rarely thought to let others know what he was up to, and his willingness to meet with executives from any other company (there were many of them trying to buy Facebook in those days) led to much anxiety in the company—no one knew whether the company would be sold or had any clue what Zuckerberg’s intentions were.

8)  He stares: “His tendency was to be quiet around strangers, but that was deceiving. When he did speak, he was wry. His tendency was to say nothing until others fully had their say. He stared. He would stare at you while you were talking, and stay absolutely silent. If you said something stimulating, he’d finally fire up his own ideas and the words would come cascading out. But if you went on too long or said something obvious, he would start looking through you. When you finished, he’d quietly mutter ‘yeah,’ then change the subject or turn away.”

9) He was a tremendous slob in college, and is specifically described as having had the bad habit of leaving food trash (cans, bottles, wrappers, etc.) wherever he happened to be when he finished with it, often leaving the trash lying around for weeks at a time (usually until his roommate’s girlfriend got fed up and took it upon herself to clean up)—inferior Se.

10) His time while in college was usually spent in his room working on his own projects (which mostly meant imagining new internet services and sometimes building them), with considerably less attention devoted to his schoolwork. The walls were covered in bits of code and formulas he’d written out, and he loved to pace about and draw out his ideas on an enormous whiteboard he had hung in the hallway. He did this at the expense of attendance to at least one of his classes, which he passed only by creating a Facebook page to solicit the class notes of his peers, which he then studied the night before the final exam. Dominant Ni/inferior Se all around.

11) When he first started living alone in California, he lived in a tiny apartment that had no furniture whatsoever except for a bare mattress on which he slept. Since he spent all his time at the Facebook offices working on his project, he saw little need for getting any furniture—again, inferior Se. (He wasn’t poor at this point, by the way. An early investment round came with a $1 million bonus, so he had more than enough to splurge on a shelf or two.)

12) Keeping his hoodie on despite sweating profusely suggests inferior Se—he’s a physically awkward and rather uncomfortable guy, and it seems as if messing with his clothing in public by taking off the hoodie would tend to throw him off his equilibrium.

13) His ostentatiously unfashionable attire in the earlier days of Facebook (especially the flip-flops-with-everything habit) which shows not even the slightest attempt to dress in a way that most people would regard as appropriate, suggests inferior Se, especially as he became increasingly important and no longer had the excuse of being a college student. His attitude was that it made no difference what  he wore if he was smart and knew what he was doing—the sort of “fuck you” to external standards and expectations that one often finds with inferior Se.

14) He lists “eliminating desire” as one of his interests on his Facebook page, which makes me think inferior Se.

15) There is good reason to believe he is a narcissist in the Millon personality scheme (though not a pathological one). Consider the Facemash incident for which he first gained notoriety at Harvard: upset over a girl for some reason (it’s not clear from his blog whether she dumped him, stood him up, or something else), he lashed out by creating a website to rate students (men and women) that pissed off nearly every women’s group on campus and the university administration. Consider the facetious megalomania of in-jokes like “I’m CEO, bitch!” and his original self-given title of “Founder, Master and Commander, Enemy of the State”—a common sort of humor for an INTJ, I think. Consider the casual arrogance of his remark he “just wished no one had made a movie about me while I’m still alive.” Consider his attitude towards venture capital firms, which he regarded with skepticism and met with a “prove yourself worthy” attitude whereas most people in his position would have been grateful for the chance to attract investor interest at all. Consider that he  is said to have had “an air about him that everything would turn out fine no matter what he did” in college. Consider Sean Parker’s observation that he has “imperial tendencies.” Consider the way he mocked the early Facebook users for being “dumb fucks” that trusted him with their personal information. Consider his arrogant decision to “fuck them in the ear” (the Winklevoss twins) by stalling development of their dating site while he built and launched Facebook. Consider his rage at learning that the Crimson was going to run a story about the Winklevosses’ accusation that he stole their idea, and the fact that he subsequently hacked into the email addresses of Crimson staff members to find out what they were going to print (the emails he saw, since released, include a comment by one Crimson staff member that Zuckerberg “seemed very sleazy” and “not very direct or open” when he visited the Crimson office to give his side of the story). Consider the fact that he hacked into the Winklevosses’ dating site to delete accounts and change users’ settings as a way of sabotaging the site—and consider that all this (the Crimson story, the hacking of emails and websites) happened several months after the launch of Facebook, by which time Facebook had many thousands of users and the Winklevoss site had almost none.

16) The evidence for inferior Fi is weak and neither sufficient to distinguish it from tertiary Fi nor enough override the evidence for inferior Se. His apparent dislike of personal questions in interviewers is not enough to distinguish between ENTJ and INTJ (or ENTP, INTP, or several other types, for that matter). The other thing you might point to is his recent habit of eating only the meat of animals he has personally slaughtered, but I’m not convinced that’s indicative of inferior Fi. It strikes me instead as a case of an aloof, brainy computer nerd taking an interest in doing something “real”—getting his hands dirty, rolling up his sleeves, doing his own dirty work; that sort of thing—which suggests to me inferior  Se. It’s the equivalent of taking up any other “hands-on” hobby, which someone whose inferior function is Se and whose time is typically spent on nerdy computer stuff and grandiose board room stuff would find invigorating—more getting in touch with his inner hunter than getting in touch with his inner child.

17)  Lastly, while this is more a context clue than an actual piece of evidence, look at the way he’s portrayed in The Social Network, which along with the book on which it’s based is basically a malicious caricature of Zuckerberg. He’s attacked in all the ways you’d think to caricature an INTJ male—malevolent loner, backstabber, weird and creepy, resentful of those who fit in better than he does, grandiose, casually arrogant and dismissive of things like friendship and other people’s intelligence, jealous of the cool kids and secretly desperate to be “one of the beautiful people,” prone to having the stilts cut out from under him by the crushingly emasculating observations of more “grounded” female characters. The story was developed in part with the cooperation of people who knew and disliked Zuckerberg, so the way in which they portrayed him tells us something about the way he is perceived by those who knew him. They portrayed him as an INTJ, so we can infer that he was perceived as such by those who knew him.

– Okay, that’s nice. But couldn’t he be INTP?

Well, against INTP We’d note that the evidence for inferior Se is strong (and that that is a strong kind of evidence); that he gave/gives the impression to those familiar with him not of schizoid remoteness/emotional deadness but of narcissistic aloofness/hidden arrogance; and that his interest in programming was, as confirmed by Zuckerberg himself, purely instrumental, not an end in itself. He only ever took interest in building websites and programs to solve real-world problems: a site that helped students pick their schedules based on who else was in each class, a program that recognized one’s taste in music, and then of course Facebook, which he built at a time when there was much talk at Harvard of having the administration build just such a service (by his own admission, he took it upon himself to upstage them). So looking at the functions directly, I see little reason to go with INTP over INTJ.